1. Field of the Invention
This invention relates to an oil pressure control valve operated by compressed air.
2. Prior Art
In the conventional dental treatment bed, for instance, the mechanism to vertically move the seat of the bed and that to tilt the back-rest forward and backward from the seat have all been operated with oil pressure. However, those employing a solenoid control valve in the oil pressure circuit for on-off control were limited to a relatively low control oil pressure, about 10 kg/cm.sup.2, and also, while the transformer was indispensable for securing the solenoid operating voltage, it frequently burnt out due to continuous use for many hours. Besides, the electrical cost was proportionally high. Because of the problems presented as mentioned above, the advent of non-electric power control type model for substituting for the solenoid type has been awaited. Also, because the compressed air-operated type parts, such as handpiece instrument, are installed in the treatment table as inseparable components, there has been another expectation attached to it that it would be doubly advantageous if the oil pressure control could be made by applying the aforementioned compressed air.